I just picked up my porcelain floor tiles from the warehouse. They were stored outside in the rain for a week. They're still wet and being aired out now. But they smell of mold. Is this bad news?
If they are true porcelain, they have not absorbed water. Porcelain are rated for exterior applications.
Some people generically call ceramic tiles porcelain, which may not be rated for continuous water exposure.
The porcelains will completely clean up and not harbor anything other than a surface covering of mold, which might have come from the packaging.
I would return them if they were given that way to you. First I would not power wash them. I know my power washer would go right through the porcelain I just installed or at the very least mark it.
Also if there is mold growing and you don't get it all off or if you don't get all of the dirt off you are taking away from the bonding area. The mold too can continue to grow after being installed. Unless you got an incredible deal on the tile I would return it.
If you have to keep it... I would mainly worry about the back of the tile and the sides. I would hit it with a bleach mixture to stop mold growth. A scouring sponge should do. If it is really that bad I might bust out an SOS pad or two. Also make sure the tiles are dry before installing.